1. Field of the Invention
The present invention relates to a termination coaxial connector comprising resistance elements and the like connected between an outer conductor and a center conductor of a coaxial line connector, and more particularly to a receptacle connector which is used as a subscriber terminal connector in a signal splitter or a signal brancher in joint viewing facilities such as CATV and TV and the like.
2. Description of the Related Arts
In joint TV viewing facilities and CATV systems, splitters and branchers having wide frequency bands are used for supplying wide-band high-frequency signals, such as multi-channel TV signals within the band 5-1,000 MHz, to subscriber houses along coaxial cables from a point on the system known as a headend. As signals are split, the signal level suffers gradual attenuation as a result of split loss and cable loss. Conventionally, in order to compensate for this attenuation, wide-band amplifiers are provided in appropriate positions for amplifying the signals to a predetermined level. The signals are subsequently retransmitted and resplit. In addition to the signals, power for the amplifiers is often supplied on the cables in a multiplexed format.
In such systems, since the branchers and splitters are provided in multilevel cascade connections, poor adjustment of the input terminals is liable to cause accumulated deterioration in the characteristics of the branchers and splitters due to the electrical length of the connection cables. As a result, the overall characteristics of the system may deteriorate severely at certain frequencies. Such deterioration in input impedance leads to phase distortion and amplitude distortion, damaging signal quality.
FIG. 9 shows a model configuration of a conventional CATV system, and FIG. 10 shows an example configuration of an electrically-powered branching/splitting circuit used in such a system. As FIG. 10 shows, high-frequency signals and electrical power are input at input terminal IN, but the electrical power, which has low frequency, is blocked by capacitors C1 and C2. Consequently, power does not flow to the branching/splitting circuit, but is instead fed along a choke coil L to an output terminal OUT. By contrast, the high-frequency signals, which are within a frequency range to which the choke coil L presents a sufficiently high impedance, are blocked by the choke coil L. The high-frequency signals therefore pass through capacitor C to the branching circuit (directional coupler), then through the other capacitor C2, and are finally output at the output terminal OUT.
However, some of the signals emerge at branch terminal B of the directional coupler. These signals may be split across 2-8 terminals (not shown in the diagram) of the splitter and their split outputs sent to subscriber houses, or the output of branch terminal B may be used directly as a trunk branch.
FIG. 11 shows an example of return loss characteristics at the input terminal of a branching/splitting circuit, in which the output ratio of input/branch terminal B is -5.0 dB, subsequently falling to -11. dB as result of a four-way split. The input impedance of this branching/splitting circuit is 75.OMEGA. at each terminal. Using as a reference the return loss (#1) at the input terminal when termination has been carried out for all the output and branch terminals with resistance of 75.OMEGA., FIG. 11 shows the characteristics when each terminal is in the open state successively, disconnecting the termination resistance of the split output terminals from terminal 1 (#2) to terminal 4 (#5). As FIG. 11 shows, when the brancher/splitter subscriber terminals include a terminal to which no lead-in wire is connected (namely, a vacant terminal) such as is shown in FIG. 10, reflected waves are returned to the input terminal of the branching/splitting circuit.
The amount of reflection differs between branchers with few branches and branchers with a comparatively large number of branches, reflection being greater when the number of branches is large. In general, CATV systems include a considerable number of vacant terminals, which are provided beforehand in anticipation of an increase in the number of subscribers after the system becomes operational. As the number of subscribers increases, the number of vacant terminals is reduced. In addition, a vacant terminal is created when a subscriber cancels his subscription.
Conventionally, reflection to the input terminal caused by such vacant terminals is prevented by connecting a terminator with a resistance element, as shown in FIG. 12, to a connector, as shown in FIG. 13.
Nevertheless, there are cases when a system includes terminals which, for some reason, are not used, yet are left open. The existence of such vacant terminals causes reflected waves, as described above, resulting in amplitude distortion and phase distortion, and damaging the quality of the signals. This can cause problems such as TV ghost images, bit errors in digital signal data services, and so on.
The receptacle connector depicted in FIG. 13 is ordinarily termed an F-type connector. F-type connectors are widely used in apparatuses for CATV systems, due to their relatively simple structure and cheap cost. An F-type connector is constructed in one piece comprising an enclosure and an outer conductor of the receptacle connector. In addition, another receptacle connector, constructed separately from the enclosure, is attached by means of crimping or screwing.
For the reasons given above, there is a need for a device, for use in CATV systems and the like, which is capable of terminating with no input reflection, without having to separately connect terminators to the vacant terminals, and which does not automatically terminate when a lead-in wire is connected. Furthermore, since the characteristics of the apparatuses are liable to be damaged at high frequency when the center conductor of the connector is connected in series with the termination resistance elements, a device which is capable of carrying out termination with only the tip portion of the center conductor of the connector is desirable in order to avoid the entry of such stray reactance into the series.
Furthermore, when the termination device has been connected, it is necessary to prevent deterioration in the overall circuit due to deterioration of the characteristics of the branching/splitting circuit upon connection of the lead-in wire. The stray reactance of the device must therefore be reduced as far as possible.